An OED refers to a device exhibiting a variety of functions through charge exchange between an electrode layer and an organic material, and includes, for example, an organic light emitting device (OLED), an organic solar cell, an organic photoconductor (OPC), or an organic transistor.
In general, an OLED, which is a representative OED, sequentially includes a substrate, a first electrode layer, an organic layer including an emitting layer, and a second electrode layer.
In a structure called a bottom emitting device, the first electrode layer may be formed of a transparent electrode layer, and the second electrode layer may be formed of a reflective electrode layer. In addition, in a structure called a top emitting device, the first electrode layer is formed of a reflective electrode layer, and the second electrode layer is formed of a transparent electrode layer.
An electron and a hole are respectively injected by two electrode layers, and the injected electron and hole are recombined in an emitting layer, thereby generating light. The light may be emitted to the substrate in the bottom emitting device, and to the second electrode layer in the top emitting device.
In a structure of the OLED, an indium tin oxide (ITO) generally used as a transparent electrode layer, an organic layer, and a substrate usually such as a glass substrate have refractive indexes of approximately 2.0, 1.8, and 1.5, respectively. Due to the relationship of such refractive indexes, for example, light generated in the organic emitting layer in the bottom emitting device is trapped by total internal reflection at an interface between the organic layer and the first electrode layer, or in the substrate, and only a very small amount of light is emitted.